feat: truncate --fields body uniformly (task 0021)

Rule that the `body` extra field truncates at 500 chars like `issue view`,
resolving the spec's Principle 3 / Command Surface contradiction. Route the
`body` extractor through a new `truncatedBody()` FieldDef so `issue list`,
`issue create`, `pr list`, and `search` all present it exactly as the detail
views do, and add a `--full` flag to each to suppress truncation, keeping the
inline hint's "use --full" promise honest.

test/search.test.ts

@@ -323,6 +323,46 @@ describe("search issues --fields", () => {
     expect(row).toContain("http://gitea.example/testowner/testrepo/issues/42");
   });
 
+  it("applies the body-truncation ruling to a match body, and --full suppresses it", async () => {
+    // Truncated inline at 500 chars with the hint.
+    server = await startFixtureServer([
+      {
+        method: "GET",
+        path: SEARCH_PATH,
+        body: [searchIssueOf(42, { body: "x".repeat(650) })],
+      },
+    ]);
+    const truncated = await runCliTest(
+      ["search", "issues", "login", "--fields", "body"],
+      { env: testModeEnv(server.url) },
+    );
+
+    expect(truncated.exitCode).toBe(0);
+    expect(truncated.stdout).toContain("x".repeat(500));
+    expect(truncated.stdout).toContain(
+      "... (truncated, 650 chars total - use --full to see complete body)",
+    );
+    expect(truncated.stdout).not.toContain("x".repeat(650));
+
+    // --full returns the body raw, with no truncation hint.
+    await server.close();
+    server = await startFixtureServer([
+      {
+        method: "GET",
+        path: SEARCH_PATH,
+        body: [searchIssueOf(42, { body: "x".repeat(650) })],
+      },
+    ]);
+    const full = await runCliTest(
+      ["search", "issues", "login", "--fields", "body", "--full"],
+      { env: testModeEnv(server.url) },
+    );
+
+    expect(full.exitCode).toBe(0);
+    expect(full.stdout).toContain("x".repeat(650));
+    expect(full.stdout).not.toContain("truncated");
+  });
+
   it("rejects an unknown --fields name with VALIDATION_ERROR", async () => {
     server = await startFixtureServer([]);